1. Field of the Invention
This invention relates to heat pump systems, and is particularly concerned with energy efficient heat pump systems for providing year-round water heating with year-round air cooling, or with seasonal air cooling, or with seasonal air cooling and heating.
2. Description of the Related Art
Any discussion of the prior art throughout the specification should in no way be considered as an admission that such prior art is widely known or forms part of common general knowledge in the field.
U.S. Pat. No. 4,766,734 describes a heat pump system for air conditioning, comfort zone heating, and water heating. Based on this system, U.S. Pat. No. 5,050,394 describes an improved heat pump system for air conditioning and water heating. Conventionally, the heat pump for air conditioning and water heating consists of a compressor for circulating a refrigerant in the system, a hot water heat exchanger for heating water, an indoor heat exchanger for conditioning and supplying air to the space to be conditioned, and an outdoor heat exchanger having an outdoor fan for dissipating or extracting heat to or from the outdoor ambient. The novel aspect of the system disclosed in U.S. Pat. No. 5,050,394 is that it also includes a means for controlling the compressor speed in accordance with the cooling load. In conventional systems, the refrigerant exhaust from the compressor enters the hot water heat exchanger first and then passes to the outdoor heat exchanger. It is stated in U.S. Pat. No. 5,050,394 that such a system may be operated in a full condensing mode in which the outdoor fan is switched off and most of the heat released from the refrigerant is used for water heating, and in a desuperheating mode in which the outdoor fan is turned on so that most of the heat released from the refrigerant is transferred by the outdoor heat exchanger to the outdoor air. However, one of the problems of such a system is that in the assumed desuperheating mode, partial condensing may occur in the hot water heat exchanger. That means the condenser temperature of the system will be raised to an unnecessarily high level (higher than the temperature of the hot water) which makes the system work in an inefficient way. On the other hand, more heat than that required to maintain the temperature of the water may be continuously transferred to the water which makes the water hotter than the set value, and the higher the water temperature, the higher the temperature of the compressor which is detrimental to the compressor. It is therefore desirable to overcome the above-mentioned problem and make the heat pump systems for water heating and air conditioning operate in a more energy efficient and reliable manner.
It is also desirable to provide heat pump systems for water heating and air conditioning which can be adjusted to meet different heating and cooling loads both economically and with little impact on each other. That is, when the heating load changes, the system should be able to be adjusted correspondingly with little impact on the cooling side, and when the cooling load changes, the system should be able to be adjusted correspondingly with little impact on the heating side.
It is further desirable to provide energy efficient heat pump systems for water heating and air conditioning which can be adjusted to work in different demanded modes such as year-round water heating and air cooling, year-round water heating and seasonal air cooling, year-round water heating and seasonal air cooling and heating.
It is an object of the present invention to overcome or ameliorate at least one of the disadvantages of the prior art, or to provide a useful alternative.